Cracks that form within materials can be difficult to detect and almost impossible to repair. A successful method of autonomically repairing cracks that has the potential for significantly increasing the longevity of materials has been described, for example, in U.S. Pat. No. 6,518,330. This self-healing system includes a material containing, for example, solid particles of Grubbs catalyst and capsules containing liquid dicyclopentadiene (DCPD) embedded in an epoxy matrix. When a crack propagates through the material, it ruptures the microcapsules and releases DCPD into the crack plane. The DCPD then mixes with the Grubbs catalyst, undergoes Ring Opening Metathesis Polymerization (ROMP), and cures to provide structural continuity where the crack had been.
Self-healing materials typically have been formed using engineering plastics, such as epoxy resins and epoxy-vinyl ester resins. Engineering plastics, in general, either fail at small deformations or are subject to permanent deformation, such as drawing, when strains become large. Cracks in engineering plastics can occur due to fatigue and/or brittle fracture.
Elastomers differ from engineering plastics in that elastomers can be subjected to large deformations and can then return to their original state with little or no permanent deformation. Applications of elastomers include seals, gaskets, coatings, adhesives, shock and/or vibration absorbers, electronics encapsulation, bladders, and vehicle tires. Crack formation in elastomers is referred to as tearing, and typically occurs at much higher strains than in engineering plastics.
Tearing in elastomers can be especially problematic. Since these materials typically are used to provide a region of flexibility to a system, they may be subjected to repeated stresses during use. Once a crack is initiated, it may grow quickly if the material is subjected to large and/or frequent stresses. If the crack is healed by the application of another polymer to the crack surface, the properties of the healed elastomer may be impaired if the mechanical properties of the new polymer and the original material are not closely matched.
It is desirable to provide an elastomer that can self-heal when subjected to a crack. It is also desirable to provide an elastomer that can maintain most or all of its advantageous elastomeric behavior after it has self-healed.